1. Technical Field
The disclosure relates to an image scanning apparatus which is included in a scanner, a photocopier, a FAX machine, a multi-function printer, and the like, and which optically scans an original placed on a platen.
2. Related Art
There is an image scanning apparatus which is included in a scanner, a photocopier, a FAX machine, a multi-function printer, and the like, and which optically scans an original placed on a platen. When the image scanning apparatus erroneously determines the original size, the image scanning apparatus can only incorrectly scan an image and may obtain defective image data such as image data partly missing. To avoid this the image scanning apparatus is equipped with an original size detection mechanism configured to detect size of an original which is a scan target.
Mechanisms configured to detect the original size in an opening closing direction (main scanning direction) in which an original cover is opened and closed include a mechanism which reads an image of an original placed on a platen glass by use of a scanning device as follows. Specifically, in a state where the original is pressed from above by a pressure plate closed, the scanning device is made to emit light and receive reflected light while performing scanning.
In this mechanism, when the light is emitted in a state where the pressure plate is open, no reflected light is detected from a portion other than an original portion (non-original portion). Accordingly, the brightness varies between the original portion and the non-original portion. There is a method of detecting the original width by using this variation in brightness between the original portion and the non-original portion (hereafter, referred to as “black portion detection method”).
The black portion detection method has the following tendency. Since reflection from a portion with high density on a print surface such as a solid black portion is low, it is likely that this solid black portion is detected as the non-original portion and erroneous detection of the original width occurs.
Japanese Unexamined Patent Application Publication No. 2007-174221 proposes a method improved to cope with the aforementioned problem. This technique utilizes a phenomenon in which reflection from the pressure plate in the non-original portion changes depending on the angle of the pressure plate in an opening-closing operation and the reflected light thus changes. In the technique, the original width is detected by detecting a boundary of the original portion and the non-original portion based on a portion in which the brightness of the reflected light changes (hereafter, referred to as “pressure plate opened-closed state difference method”). In the “pressure plate opened-closed state difference method,” reading is triggered by detection by a sensor for detecting a pressure-plate semi-open state (middle angle sensor) and is performed in the pressure-plate semi-open state. When a predetermined time elapses from this reading, reading is performed again in a pressure-plate closed state (a state where the pressure plate is further closed from the semi-open state but is not completely closed). Pieces of read data (middle angle data and small angle data) obtained at two angles in the course of completely closing the pressure plate are compared with each other to detect a portion with the brightness difference, and the original width is calculated with the boundary between the original portion and the non-original portion determined based on the portion thus detected. The pressure plate opened-closed state difference method utilizes the brightness difference occurring between opening-closing stages of the pressure plate due to change in reflection from the pressure plate during the opening-closing operation, and can detect the original width regardless of the color of the sheet, the density of the print surface, and the like.